It was not the most diplomatic way to start a summit of world leaders. On Sept. 4, the day before Russian President Vladimir Putin begins hosting the G-20 summit in his hometown of St. Petersburg, he accused the Obama Administration of lying to Congress, and said U.S. lawmakers were being suckered into approving a military strike against Syria. “We talk with these people. We assume that they are decent. But he lies,” Putin said of U.S. Secretary of State John Kerry. “And he knows that he lies. That’s pathetic.”

The remarks, which seemed more fitting for a barroom scrap than a Kremlin statement, came on the eve of an urgent global debate about how to respond to the Syrian regime’s alleged use of chemical weapons near Damascus last month. At least with regards to that issue, Putin’s tone left little room to hope for compromise, or even civility, at the G-20 or on its sidelines. President Barack Obama still put on a brave face as he headed to St. Petersburg on Wednesday, retaining some optimism about the prospects of the Kremlin changing its line on the Syrian question. “Do I hold out hope that Mr. Putin may change his position on some of these issues? I’m always hopeful, and I will continue to engage him,” Obama said at a press conference in Sweden, which he was visiting before continuing on to Russia.

In the lead up to G-20, there has been considerable tension between the White House and the Kremlin. Last month, Obama canceled a meeting with Putin that was scheduled for the eve of the summit, the first time that talks between the U.S. and Russian leaders had been called off in 53 years. Citing deadlock on everything from human rights to nuclear nonproliferation — as well as Russia’s decision in July to grant asylum to the fugitive American whistleblower Edward Snowden — Obama said his Administration was taking a “pause” in relations with Russia. Adding insult to injury, he said that Putin’s slouching posture at their previous meetings was like that of a “bored kid in the back of the classroom.”

For weeks, Putin avoided hitting back, with the Kremlin saying only that it was “disappointed” by Obama’s decision. On Tuesday, Putin even seemed to extend an olive branch. In an interview with the Associated Press, Putin said he did not “rule out” Russia backing a military strike against Syria, a longtime Russian ally. But he set one “absolutely principled condition” for such a move: the U.N. Security Council, where Russia has veto power, must be shown incontrovertible proof that the chemical attack near Damascus was orchestrated by the Syrian government, as the White House has claimed. Any foreign attack against Syria that does not have U.N. approval, Putin said, “cannot be qualified as anything other than aggression.”

But the overall message of that interview — in which Putin advised the U.S. to “not get annoyed, store up some patience and work toward finding solutions” — left the door open for reconciliation at the G-20. The next day, however, that seemed to go out the window. At a meeting with his human-rights council in the Kremlin, Putin said he had watched Kerry make his case for a strike against Syria to U.S. lawmakers, who are expected to vote on whether to allow the attack in the coming days. “Of course he lied. And that’s not pretty,” Putin said.

He claimed that Kerry misled U.S. lawmakers by asserting that al-Qaeda was not present in Syria — an assertion that Kerry did not actually make during his testimony to the Senate Foreign Relations Committee on Tuesday. According to Reuters, a Senator asked Kerry whether it was “basically true” that Syria’s rebels had “become more infiltrated by al-Qaeda over time,” to which Kerry responded, “No, that is actually basically not true. It’s basically incorrect.” But the impression that Putin got from that exchange was “not very pleasant for me,” the Russian President said.

Even less pleasant, perhaps, will be the job of trying to get something done at the G-20 summit amid all the backbiting. While many of the top delegates will be tangled up in the Syria debate on the sidelines, the summit’s formal agenda has set out to reach global accord on how to fight tax havens, create jobs and boost the world’s sluggish economic recovery. The responsibility for making delegates pay attention to these goals will fall in large part on Ksenia Yudaeva, Russia’s representative at the G-20. About two weeks before the summit commenced, she took TIME on a golf-cart ride around the Konstantin Palace, the former residence of the Russian czars that will serve as the venue for the summit, and as the palace gardens flitted past, Yudaeva was still holding out hope that the G-20 could focus on the global economy. “At least the last couple of times, the whole agenda was pushed to the background because something exploded,” she said.

Previously that had been the financial meltdown in Greece, which occupied the attention of the G-20 leaders’ summit last year. “This year we did everything we could to avoid that,” said Yudaeva. But with U.S. missiles poised to strike at a key Russian ally, keeping the focus on the G-20’s economic agenda may be a lost cause – about as likely as making Putin and Obama see eye to eye at the summit. And although the weather is forecast to be clear this week in St. Petersburg, the mood inside the Konstantin Palace will likely be as cold as a Russian winter.